MONDAY, Sept. 24 (HealthDay News) -- More and more children are growing up with autism, and although many treatments and interventions are now available, clinical studies on the use of medications in teens and young adults are lacking, according to new research.

"The majority of (older) individuals with autism spectrum disorders appear to be taking medications that we have very little evidence for," said the study's lead author, Dr. Jeremy Veenstra-VanderWeele, medical director of the Treatment and Research Institute for Autism Spectrum Disorders at the Vanderbilt Brain Institute in Nashville, Tenn.

"In the absence of sufficient evidence, parents and people with autism should find a clinician who tells you what's known and unknown about the potential benefits and risks of any medication," he said. "It should be a shared decision-making process."

Results of the study were published online on Sept. 24 in the journal Pediatrics.

Autism spectrum disorders are neurodevelopmental disorders that impair social development and communication. Autism spectrum disorders also may cause repetitive movements and even self-abusive behavior, such as head banging, according to the U.S. National Institute of Neurological Disorders and Stroke (NINDS).

It is estimated that about one in 88 American children has been identified with an autism spectrum disorder

As children with autism age, some do experience significant improvements, according to NINDS, but many do not. There is no cure for autism, although there are many treatments available, including education and behavioral interventions and medications.

Medications usually are used to treat some of the symptoms associated with autism, rather than the core symptoms of the condition, according to background information in the new study. For example, the medication risperidone (brand name Risperdal) may be used to treat behavioral symptoms associated with autism, such as aggression, outbursts and irritability, said Dr. Melissa Nishawala, medical director of the Autism Spectrum Disorders Clinical and Research Program at the NYU Child Study Center in New York City.

"Medications like risperidone and aripiprazole don't address the cause of autism, but they help calm down [people with autism]," Veenstra-VanderWeele said.

For the new study, the researchers reviewed medical literature from 1980 through 2011 to find clinical trials on drugs for people with autism between the ages of 13 and 30 years old. They found eight studies with at least 20 participants. Two investigators independently assessed the quality of the studies.

The researchers said they found four studies of fair quality while the other four were poor. The studies included reviews of antipsychotic medications, such as risperidone and haloperidol (Haldol); serotonin reuptake inhibitors, such as fluvoxamine (Luvox) and clomipramine (Anafranil); and opioid receptor antagonists, such as naltrexone (Depade).

The researchers felt that, overall, there wasn't enough data on medications in the teen and young adult autism population. Risperidone wasn't well studied in teens and young adults, but there was evidence for its use if the entire pediatric population was considered, the study said.

Although behavioral and educational interventions weren't included in the new study, Veenstra-VanderWeele said he suspects there's a lack of evidence for these types of treatments in older children and young adults too.

"We really don't know if intensive behavior interventions continue to benefit individuals as they get older," he said.

NYU's Nishawala said: "The most important thing for parents to take away is that we know there are a few medications that have been studied that can help. Certain symptoms like irritability, agitation and aggression can be controlled with medications, but there's lesser evidence that repetitive behaviors can be treated."

Nishawala added that although she and others who treat older children and young adults with autism would love to have more evidence-based research on the medications they use, it can be difficult to get parents and older children to participate in clinical trials when medications are already available to them for what's known as "off-label" use. That's when doctors prescribe medications for a condition for which the drug has yet to receive U.S. Food and Drug Administration approval.

In addition, she said, it's difficult to get funding for trials, particularly when a drug already has been approved.

More information

Learn more about autism and teens from the Nemours Foundation.